The intent of this project is to develop new and improve existing instrumentation and to develop new experimental and data analysis methods for the characterization of biological macromolecules and the study of their interactions. In the area of the analysis of the data from analytical ultracentrifugation, further extentions have been made in the major breakthrough achieved by the use of light intensity data rather than light absorbency data from the analytical ultracentrifuge. The intensity data is advantageous because of its superior statistical properties and its potential to provide better parameter estimates in ultracentrifugal analyses. The extentions in this method have been in the applications of Monte Carlo methods for the estimation of the errors in the parameters obtained when fitting data by non-linear least-squares curve-fitting. Work on other statistical measures of error analysis is under way. Additional experience with this method has been gained, as it has continued to be extensively applied to the study of the association of DNA repair enzymes, as well as to other interacting systems studied in a variety of collaborative projects. The intensity approach has been particularly useful for multiwavelength analyses of protein-DNA interactions, reducing the time for multiwavelength data acquisition by at least a third, and reducing the data processing and analysis time by more than half, while achieving enhanced accuracy at the same time. - analytical ultracentrifugation, data analysis fitting parameter error estimation, scanning system